"Our priority is safety with Hurricane Iselle coming. Please take down your signs and banners so they don't become a hazard," Schatz tweeted Wednesday night.

"We are monitoring the situation closely. Sen. Schatz is first and foremost a United States senator, so his primary concern is people's safety," Schatz spokeswoman Meaghan Smith told The Hill.

Hanabusa emailed supporters asking them to take precautions, and announcing the cancellation of events.

"In the interest of safety, we are asking all of our supporters to take down their Hanabusa signs and banners. High winds may be able to dislodge signs, banners, and stakes," she wrote in a campaign email. "Until further notice, we are canceling all of our signwavings across the islands out of respect to our volunteers and drivers who may have to navigate inclement weather."

The hurricane is expected to be the first in more than two decades to directly hit Hawaii, though meteorologists are predicting that the storm's force will lessen as it approaches the islands and will be downgraded to a tropical storm. Hurricane Julio is hot on its heels and is expected to hit Hawaii on Sunday.

The storm could scuttle last-minute get-out-the-vote operations for the two campaigns, as well as the competitive gubernatorial primary between Hawaii Gov. Neil Abercrombie (D) and Hawaii state Sen. David Ige (D), and the primary for Hanabusa's House seat.

Schatz has led Hanabusa in most public polling, though Hawaii polls are notoriously unreliable.

President Obama was briefed Thursday morning about the storms and preparations by Homeland Security adviser Lisa Monaco. The Federal Emergency Management agency has deployed an incident management team to the state and White House officials are in "close contact" with officials there, press secretary Josh Earnest said.

"These are powerful storms with the potential to cause significant damage, so we — as we often do in these circumstances — strongly encourage those in the path of the storms to take appropriate steps to prepare and to heed the warnings of state and local officials," Earnest said.